The invention relates to the field of the acceleration of material, in particular a stream of granular or particulate material, with the aid of centrifugal force, with, in particular, the aim of causing the accelerated grains or particles to collide at a speed such that they break.
According to a known technique the movement of a stream of material can be accelerated with the aid of centrifugal force. With this technique the material is introduced into the central chamber of a rotor and is then picked up by guide elements which are arranged around the central chamber and are supported by the rotor. Normally such a rotor rotates about a vertical axis of rotation; however, rotation can also take place about a horizontal axis. The material is accelerated along the guide elements and propelled outwards at high speed and at a certain angle of flight. The angle of flight is usually barely affected by the speed of rotation and is virtually constant for the individual grains in a granular stream. The speed which the material acquires during this operation is determined by the speed of rotation of the rotor. The speed of flight is composed of a radial speed component and a speed component oriented perpendicularly to the radial, or transverse speed component.
Viewed from the stationary standpoint and when the influence of air resistance and air movements are disregarded, the material moves at virtually constant speed along a virtually straight stream after it has left the guide element. This straight stream is directed forwards, viewed in the direction of rotation, and the magnitude of the angle of flight is in this case determined by the magnitudes of the radial and transverse speed components which, in turn, are determined by the length and positioning of the guide element and the coefficient of friction. If the radial and transverse components are identical, the angle of flight is 45xc2x0.
Viewed from a standpoint moving with the guide element, the material moves in a spiral stream after it leaves the guide element, which spiral stream is oriented backwards, viewed in the direction of rotation, and is in the extension of the guide element. In this case the relative speed increases as the material moves further away from the axis of rotation.
The material can be propelled outwards in this way, with the aim of distributing or spreading it regularly; for example salt on a road or seed over agricultural land.
The material can also be collected by a stationary impact element that is arranged in the straight stream which the material describes, with the aim of causing the material to break during impact. The stationary impact element can be formed, for example, by an armoured ring which is arranged around the rotor. The comminution process takes place during this single impact, the equipment being referred to as a single impact breaker.
Research has shown that for the comminution of material by means of impact stress a perpendicular impact is not optimum for the majority of materials and that, depending on the specific type of material, a higher probability of break can be achieved with an impact angle of approximately 75xc2x0, or at least between 70xc2x0 and 85xc2x0. Furthermore, the probability of break can also be appreciably increased if the material to be broken is exposed not to single impact stress but to multiple, or at least double, impact stress in rapid succession. What is most important, however, is that the impact or impacts as far as possible take place free from interference.
Such a multiple impact can be achieved by, instead of allowing the material to impinge directly on a stationary impact element, first allowing the material to collide with an impact element that is moving with the guide element, that is rotating at the same speed, in the same direction and around the same axis of rotation, but at a greater radial distance from the axis of rotation than the guide element and is arranged transversely in the spiral stream which the material describes. Because the impact takes place essentially deterministically, the impact surface can be arranged at an angle such that the impact takes place at an optimum angle. The material is simultaneously stressed and additionally accelerated by the impact on the moving impact element before it impinges on the stationary collision element. With this arrangement both the acceleration and the impact take place in two steps, this equipment being referred to as a direct multiple impact breaker. With this arrangement it is possible then to allow the material to impinge on a further moving impact element which is arranged an even greater distance away from the axis of rotation.
It is thus possible to bring material into motion with the aid of centrifugal force and then to subject it to single or multiple stress in various ways.
The invention described here relates to a rotor which rotates about an axis of rotation, by means of which material, in particular a stream of granular material, is accelerated with the aid of a guide element that is supported by the rotor, with the aim, in particular, of allowing the material to collide at such a speed that the material breaks. The rotor described here can be arranged in a comminution installation, for example a breaker or a mill, but can also be arranged in a distributor or spreader device.
In the known single impact breakers the impact surfaces of the stationary impact element are in general so arranged that the impact with the horizontal surface takes place perpendicularly as far as possible. The consequence of the specific arrangement of the impact surfaces necessary for this is that the armoured ring as a whole has a sort of knurled shape. Such an installation, which is equipped with a rotor which rotates about a vertical axis of rotation, is disclosed in U.S. Pat. No. 5,921,484.
PCT/NL 97/00 565, which has been drawn up in the name of the Applicant, discloses a method and installation for a direct multiple impact breaker which is equipped with a rotor which rotates about a vertical axis of rotation, by means of which the material is accelerated in two steps, these being, respectively, guiding over a relatively short guide element and impact by a moving impact element, in order then to be allowed to impinge on a stationary impact element in the form of individual evolvent impact elements which are arranged around the rotor. Stressing thus takes place in two immediately successive steps. The second impact takes place at a speed, or kinetic energy, which remains after the first impact, that is to say without additional energy having to be supplied. This residual speed is usually at least equal to the speed at which the first impact takes place. The stationary collision element can comprise an armoured ring or a bed of own material, whilst some of the material can be guided along the stationary collision elements bypassing the rotor.
U.S. Pat. No. 4,083,504 (Wattles et al.) discloses an apparatus with a rotor rotating about a vertical axis of rotation where the material is metered on the rotor with two upstanding chutes which are a distance away from the axis of rotation. This makes it possible to support the rotor with a shaft which is mounted on top of the rotor between the chutes; which results in a rotor which is hanging free above the hopper. As a whole this results in a more compact construction and makes the axis and drive and rotor more easily accessible. A problem is that the material has to be fed to the rotor a distance away from the axis of rotation because the shaft is in the middle. To obtain a reasonable regular distribution of the material to the rotor, in such a way that the material is spread all around the rotor to be accelerated and to impact against the circular series of depending fixed impactors that are positioned around the rotor, the material is fed to the rotor through at least two chutes which are mounted opposite of each other, and the bottom of these chutes are preferably directed angled towards the axis of rotation and attached to a coverbox having two holes for the chutes to meter the material to the centre of the rotor and a hole for the axis.
The known rotors have the advantage that when the material is picked up by the guide elements it is effectively accelerated and propelled outwards in a targeted manner, it being possible accurately to adjust the speed with the aid of the speed of revolution. Furthermore, the construction is simple and both small and relatively large quantities of granular material having dimensions which range from less than 1 mm to more than 100 mm can be accelerated. The known impact breakers also have a number of advantages. For instance, the breakers are simple and consequently not expensive to purchase. The direct multiple impact breaker in particular has a high comminution intensity. The known direct multiple impact breaker has a comminution intensity at least twice as high as that of the known single impact breaker, incidentally for the same energy consumption. In addition to these advantages, the known rotors and breakers are also found to have disadvantages. For example, as a result of the centric nature of the known rotors the material is propelled outwards in all directions around the rotor, which constitutes a problem if it is desired to direct the material in a specific direction away from the rotor. In the case of comminution installations the material stream collides with a stationary armoured ring and the edges of the projecting corners of the armoured elements partially interfere with the impacts. These interfering influences are fairly large, although very much lower in the direct multiple impact breaker than in the single impact breaker. In the direct multiple impact breaker the first collision takes place undisturbed against the moving impact element, without the material leaving the rotary environment. In the case of projecting corners of armoured elements in a single impact breaker the interference effect can be indicated as the length which is calculated by multiplying the diameter of the material to be broken by the number of projecting corner points on the armoured ring relative to the total length or the circumference of the armoured ring. In the known single impact breakers often more than half the grains in the material stream are subject to an interference effect during impact. This interference effect increases substantially as the projecting corners become rounded under the influence of wear.
These interference effects have a substantial influence on the probability of break, which declines sharply as the interference effect increases. Therefore, the collision speed usually has to be increased in order to achieve a reasonable degree of comminution, which demands additional energy and causes wear, and thus the interference effect, to increase even more substantially, whilst an undesirably high number of very fine particles can be produced. The consequence of these various aspects is that the comminution process is not always equally well controllable, as a result of which not all particles are broken in a uniform manner. As a result the broken product obtained frequently has a fairly wide spread in grain size and grain configuration.
The centric nature constitutes another disadvantage of the known impact breaker. After all, the material is metered in a stream into the central chamber of the rotor and from there is uniformly distributed around the rotor blade and accelerated in order then to be propelled outwards in all directions from the edge of the rotor blade like a fan onto a stationary impact element. The material drops down after this collision and, as it were, forms an all-round cylindrical curtain, which is collected beneath the rotor in a funnel with the outlet in a region centrically below the rotor. Therefore, the space above, around the outside of and beneath the rotor must as far as possible be kept free so that the granular traffic is not impeded. If the shaft of the rotor is continued upwards this hinders metering. The shaft can therefore only be mounted on bearings below the rotor, which yields a less stable construction. A second bearing above the rotor would yield a much simpler and more stable construction. If the shaft is continued downwards this impedes the discharge. The shaft therefore has to be supported on the side walls of the breaker, which demands a fairly heavyweight construction which has to be mounted in the breaking chamber. The funnel construction which, because of its large diameter, has to be made relatively high, therefore has to be arranged further towards the bottom, which requires even more height in the overall construction. Finally, the shaft must be driven by a motor which has to be set up in its entirety outside the breaking chamber, which demands relatively long V-belts which have to be fed in a tubular construction through the breaking chamber. Direct drive is essentially not feasible. All of this means that the construction cannot be optimised and has to be made fairly heavy and high, whilst the passage of the material is also impeded by the various auxiliary constructions.
The aim of the invention is therefore to provide a method and an installation, as described above, having a rotor which does not have these disadvantages or at least displays these disadvantages to a lesser extent. The aim is achieved by propelling the material, after it has been metered onto the rotor, distributed and accelerated, not outwards in all directions around the rotor but in at least one separate flow region which is located at a fixedxe2x80x94that is immobilexe2x80x94location, viewed from a stationary standpoint, which is not influenced by the speed of rotation, after which the material is either struck once with the aid of at least one stationary impact element that is arranged in the flow region, or collides twice in immediate succession in the flow region with the aid of at least one moving collision element which is associated with the guide element and at least one stationary collision element, which collision elements are both arranged in the flow region, and is further described in the claims, to which reference is made.
The method and installation of the invention make use of the fact that the movement of the material, from the point in time when the material is picked up from the central chamber of the rotor by the guide element and is then accelerated and propelled centrifugally outwards, follows an entirely deterministic path (as is described in detail in PCT/NL 97/00656), in other words:
that the location where the material is picked up from the central chamber by the guide element determines the flow region in which the material moves further;
that the material stream which is fed continuously to the guide element continues to move in the flow region;
that the direction of movement of the material in the flow region is not influenced by the speed of rotation of the rotor.
This makes it possible to accelerate the granular material and then to guide it into one flow region which is located at a fixedxe2x80x94that is immobilexe2x80x94location which is not rotating with the rotor and is not influenced by the speed of rotation and to cause the material to undergo a single collision or multiple collisions in the flow region.
With the method according to the invention the rotor carries at least one guide element that is provided with a guide surface having a start edge and an end edge, which guide element extends in the direction of the outer edge of the rotor. When the rotor rotates the start edge, which is located a radial distance away from the axis of rotation, forms an imaginary revolving body, within which the start edge revolves and the axis of revolution of which is coincident with the axis of rotation of the rotor, and this so-called first revolving body as it were determines the central chamber of the rotor. If the start edge is oriented perpendicularly to the rotor or the plane of rotation, the central chamber is of cylindrical shape. If the start edge is oriented at an angle, the shape is conical. The material is metered into at least one metering region with the aid of a stationary metering element that is provided with at least one metering port, which metering region is determined on the rotor in a fixed location, viewed from a stationary standpoint, on a position in a sector of the first revolving body, which sector is determined by the space between two radial surfaces from the axis of rotation and the two parallel circles which delimit the first revolving body. The stationary metering element can comprise a type of funnel, tube or channel construction which is provided with one or more outlets which act as metering ports. Once in the sector, the material moves outwards in virtually the radial direction. Specifically, the surface of the central chamber is revolving so rapidly that the grains essentially do not sense it or barely sense it. (This behaviour can be compared with pulling a tablecloth very quickly from a table laid with crockery; if this is done quickly enough the crockery remains in place). During this movement the grains therefore move from the metering region, which is located a smaller radial distance away from the axis of rotation than is the edge of the central chamber (first imaginary revolving surface), in the radial direction towards a feed region which is located a greater distance away from the axis of rotation than is the edge of the central chamber. During this movement the grains therefore have to pass the outer edge of the central chamber, or the first revolving surface. In essence there can be said to be a first imaginary window in the revolving surface, the periphery of which is determined by the section (arc) of the first revolving surface that describes the sector. In the feed region, which is located close to but just beyond the first window, the material is picked up by the guide element when the latter passes through the feed region. The location where the material passes through the first window now determines the further direction of movement, or flow region, along which the material moves when it is accelerated along the guide surface, leaves the guide element at the end edge and then is propelled outwards through a second window in a second revolving surface that is formed by the revolving body in which the end edge is revolving. The first section of the flow region in which the material is accelerated along the guide surface is oriented forwards, is spiral in shape, and extends from the first window towards the second imaginary window, by means of which the location is determined. The second section of the flow region, in which the grains move when they leave the guide element, is straight and oriented forwards. The location is determined by the angle of flight at which the material leaves the guide element. There is thus a flow region which is located in a fixed location. The second section of the flow region can, incidentally, also be regarded from a standpoint moving with the guide element, in which case the flow region is spiral in shape and oriented backwards.
The feed of material to the guide element takes place only at the location of the edge of the sector, or through the first window, and is therefore continually interrupted. Material is picked up only at the point in time when the guide element crosses the stream along which the material is directed outwards, or the feed region, the next portion is picked up by a following guide element at the point in time when the latter crosses the feed region, etc. A specific stream of material which is fed through the first window to the feed region is thus distributed over various guide elements and successive portions from the respective streams which cross the guide element then move along a specific guide element. It is possible to equip the rotor with a single guide element; the material is then picked up in successive portions during each revolution.
Thus, the stream of material moving outwards along the guide element is not a continuous stream but a discontinuous stream which consists of successive portions of the stream of material, or material portions, with free spaces between them. The magnitude of the free spaces is determined by the number and the width, around the periphery, of the first revolving body. As a result of the acceleration both the length of the material portions and of the free space increase along the guide surface as the material becomes further removed from the axis of rotation. At the location of the end edge the material leaves the guide element and the material portions are propelled successively outwards along a flow region. As a whole one or more flow regions which widen towards the outside and in which the respective material portions move outwards as individual particle streams are produced in the breaking chamber, which regions are interrupted by empty space all round. Each of these streams can be collected by an impact element mounted such that it is stationary, which impact element is arranged in an impact location with the impact surface directed transversely to the direction of movement described by the material in the straight flow region concerned, viewed from a stationary standpoint; however, the material can also first be accelerated by a moving collision element associated with the guide element, which collision element is arranged in a collision location with the collision surface directed transversely to the direction of movement of the material in the spiral flow region, viewed from a standpoint moving with the guide element, after which the material is further guided, when it leaves the moving collision element, into a third straight section of the flow region, in the direction of a stationary collision element that is arranged in a collision location with the collision surface oriented transversely to the direction of movement of the material in the third flow region.
Thus, viewed from a stationary standpoint, the location where the material is picked up by the guide element determines the location at which the material leaves the guide element and the location where the material collides with the stationary collision element and optionally, in between these, the location where the material collides with one (or more) moving collision elements.
As has been stated, the sector in which the material is metered into the central chamber describes a first mid-point angle. The flow region widens as the material becomes further removed from the axis of rotation. The paths described by the material portions which are picked up by the guide element each time the latter passes through the flow region are always located in the flow region in a position between two radial planes from the axis of rotation which describe a mid-point angle which is approximately equal in size to but not smaller than the first mid-point angle. The impacts between the moving and stationary collision elements therefore also always take place between two radial planes from the axis of rotation which describe a mid-point angle which is no greater than the first mid-point angle.
The method of the invention makes an installation possible which has a rotor which rotates about an axis of rotation which can have been arranged either vertically or horizontally, whilst the rotor essentially is also able to rotate about an axis of rotation arranged at an angle.
Equipped with a vertical shaft, a type of eccentric cross-flow breaker is produced as a whole. After all, there is material which is metered at a metering location eccentrically from the axis of rotation and then moves outwards as particles along a stream transversely through the breaker, which particles then collide with one stationary collision element that is arranged eccentrically at a location outside the rotor. The abovementioned centric nature of the impact breaker is thus dispensed with, which makes the construction and the feed and discharge of material much simpler.
The disadvantage of such an eccentric construction is the capacity, which is restricted because the material has to be guided outwards from the distributor element through one window in a single stream. The capacity of the window can be appreciably increased by allowing the distributor element to vibrate or jolt or otherwise to move, in its entirety or at the location of the port, so that the throughput is promoted. The method of the invention also provides the facility for metering the material at high speed and in a more targeted manner at the metering location, so that the material is guided into the desired stream at high speed and more material, or larger portions of the stream of material, are picked up by the guide element at the point in time when this crosses the stream of material. This is achieved by guiding the material outwards from the conveyor belt with the aid of a distributor element in the form of a sloping channel construction, optionally a vibrating channel, which is directed onto the distribution location and, if possible, also arranging the conveyor belt in the extension of this stream.
The invention provides the facility for continuing the shaft upwards and providing it with additional bearings without feeding and metering being impeded, whilst the shaft can be supported directly on a foundation construction below the rotor, without the discharge being impeded, the material stream being collected, after it has collided with the stationary collision element, at a location beyond the rotor and discharged. A small funnel can suffice for this purpose, whilst the conveyor belt, by means of which the material is discharged, does not have to be continued to below the rotor. This makes it possible to make such an eccentric impact breaker of relatively simple, less high and compact construction, with a relatively lightweight shaft construction, with lighter-weight bearings, without heavy support constructions and without a large funnel construction. This makes the breaker outstandingly suitable for a mobile set-up.
The invention also provides a facility for supporting the shaft construction on a support construction that is housed in a support sector of the circular chamber around the axis of rotation. This support sector normally describes a mid-point angle which is no greater than 90xc2x0 to 180xc2x0, but it is also possible to restrict this to 30xc2x0. In essence, the support construction (sector) can be continued to the edge of the rotor. What is achieved by this means is that after the material has impinged on the stationary impact element it is able to drop down freely in the region beyond this support sector and is not impeded by support and drive constructions. Only the material that impinges on the stationary impact element in a region above the support sector has to be guided downwards over this sector. This method of construction has the advantage that the shaft construction can be supported easily because the space beneath this support sector can be fully extended towards the bottom and provided with foundations. The easy accessibility of such an open support sector also makes it possible to provide the shaft with a direct drive in this space.
Equipped with a horizontal shaft, this shaft can be supported and provided with bearings on one side or on both sides of the rotor. Here the first window through which the material is guided from the central chamber to the guide element is usually determined, under the influence of gravity, in the lower half of the central chamber. With this arrangement it is preferable, but this is not essential, to construct the central chamber in the form of a type of stationary, approximately half-open drum, the bottom open section of which acts as the window. The material is guided through this window to the guide elements. In other respects the mode of operation is essentially the same as that for an installation constructed with a vertical shaft.
The invention provides a facility for guiding the material outwards from the central chamber into more than one flow region. This is achieved, for example, by constructing the metering element with multiple metering ports by means of which the material is metered into several sectors in the central chamber. It is also possible to distribute the material with the aid of a stationary distributor element from the central chamber over multiple feed regions. Such a distributor element consists of a number of stationary deflector elements which are arranged in a position along the central chamber. The material is directed outwards from the central chamber in a number of streams between these stationary deflector elementsxe2x80x94or, as it were, through ports. The stationary deflector elements can be constructed in the form of circular or triangular rods; in each case such that no material can adhere thereto under the influence of midpoint centrifugal force and at least not such that the passage of the material is impeded by this centrifugal force. If the central chamber is arranged such that it is stationary, the deflector elements can be supported by the metering surface. The deflector elements can prevent the passage of the material, or grain traffic, through the ports. Because these have been arranged such that they are stationary, the deflector elements, but also the entire distributor element, can be brought into vibration, or into a jolting state, in a relatively simple manner, by which means the throughput of material is promoted. Once it has been guided outwards through the port, the stream of material is picked up in portions by one or more rotary guide elements at the feed locations, which are located in a position just outside the ports.
The method of the invention thus makes it possible to guide the stream of material, with the aid of a distributor element, outwards from the metering region of the rotor to positions such that the streams of particles do not strike the projecting corners and edges of the moving impact elements and stationary collision elements: these are, as it were, xe2x80x9cmaskedxe2x80x9d with the aid of the deflector elements. The interfering effect which can be caused by these projecting corners and edges is consequently virtually eliminated. The method of the invention thus makes it possible so to synchronise the movement of the material and the impact element that the material is successively stressed several times in an (essentially deterministic) manner, free from interference, it being possible accurately to control the speed at which the successive collisions take place with the aid of the angular speed.
What is achieved in this way is that the probability of break is appreciably increased, the energy consumption is reduced, as is the wear, and a break product of uniform quality is produced.